The present invention relates to an automatic hub clutch used for connection and disconnection of a drive axle with a wheel of a four-wheel drive vehicle and more particularly, to a hub clutch which is simple in construction and which has a short axial length, compared to that of the prior art.
Heretofore, various types of hub clutches have been used for engaging a drive shaft or axle with associated wheels of a four-wheel vehicle. For example, U.S. patent Ser. No. 27,347 filed Apr. 5, 1979, corresponding to U.S. Pat. No. 4,281,749, discloses an automatic locking clutch comprising a return spring restricting the axial movement of a slide gear, and a thrust transmission or load spring. The return spring and the load spring are disposed axially forward and backward of the slide gear, respectively. Upon development of thrust, the return spring is compressed by a plurality of fingers extended through the slide gear to permit the slide gear to move in its axial direction, thereby engaging the slide gear with a driven gear to provide a four-wheel drive mode.
According to this clutch, the return spring can restrict the axial movement of the slide gear unless an axial thrust higher than a predetermined level is applied by a cam. Therefore, spurious movement of the slide gear may be prevented by the action of the return spring, even upon an increase in viscous drag of lubricating oil resulting from a decrease of atmospheric temperatures or upon development of gravity or forces in the lateral direction resulting from sudden cornering of the vehicle and the like.
However, such an automatic locking clutch has problems in that the axial length of the clutch is large because of the return spring, the slide gear and the thrust transmission spring are arranged axially in series with each other, and the fingers extended through the slide gear and its associated structure make the construction of the clutch very complicated. The large axial size of the clutch results in a legal problem due to protruding of the rotating portions out of the outside width of the vehicle, the problem that the protruded rotating portions are subject to damage upon off-load running, and so forth.